Geology and geochemistry of the Dengjiashan Zn–Pb SEDEX deposit, Qinling Belt, China
Bibliographic record
Abstract
Dengjiashan, with 25 Mt at 4.77% Zn, 1.27% Pb, and 14 g/t Ag, is one of the largest SEDEX (sedimentary-exhalative) Zn–Pb sulfide deposits in the western Qinling orogenic belt, China. The ore is hosted in chert stratigraphically conformable with underlying bioclastic micrite and overlying phyllite of an intensely folded and faulted Middle Devonian sedimentary sequence. The fact that the major orebodies are located between platformal limestone and overlying phyllite indicates that mineralization took place when the Dengjiashan sedimentary sub-basin subsided from an open platform to a shallow-marine basin within an extensional tectonic setting. The deposit comprises 16 sulfide orebodies, of which the #1 and #9 orebodies are the two largest and account for 95% of ore reserves. The massive sulfide lenses are mainly composed of sphalerite, pyrite, and galena, with minor chalcopyrite, tetrahedrite, cinnabar, pyrargyrite, freibergite, boulangerite, polybasite, and trace amounts of owyheeite and native gold. The gangue is dominated by quartz, calcite, barite, and ankerite, with minor amounts of sericite, chlorite, celsian, cymrite, and albite. The rare-earth element patterns of sulfide beds and host chert suggest that the mineralizing fluids were dominated by oxidized seawater that leached Eu from feldspar in basement rocks. Strontium isotopes also suggest that the hydrothermal fluids were composed of Devonian seawater that leached radiogenic Sr along the flow path. Lead isotope ratios form an array between the upper crust and orogene curves in the 207 Pb/ 204 Pb– 206 Pb/ 204 Pb diagram, indicating that lead was leached from crustal rocks below the deposits. Sulfur isotopes indicate that bacterial sulfate reduction (BSR) sulfide formed in a sub-basin restricted to sulfate where it mixed with heavy hydrothermal sulfur from thermochemical sulfate reduction (TSR) of Devonian seawater sulfate.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".